This invention relates to a method of and apparatus for oxidizing p-xylene, and in particular, to the use of an induced flow loop reactor for the oxidation of p-xylene and/or p-methyltoluate.
Various reaction sequences, methods, and apparatus for the oxidation of p-xylene, p-toluic acid, and esters thereof, to form terephthalates including dimethylterephthalate (DMT), are known. For example, U.S Pat. No. 4,185,073, teaches an apparatus for continuous production of terephthalic acid by catalytic air-oxidation of p-xylene in a benzoic acid-water liquid solvent system. U.S. Pat. No. 3,923,867, teaches a method of producing high purity monomethylterephthalate by oxidation of p-xylene. Various methods of producing terephthalic acid from p-xylene are taught in U.S. Pat. Nos. 3,513,193; 3,887,612; and 3,850,981.
The oxidation products of p-xylene have wide commercial and industrial application, particularly in the production of polyester fibers and films. Industrial-scale methods and apparatus for oxidation of p-xylene are known, but none to date achieve high yields and good temperature control utilizing relatively simple and inexpensive equipment.
Moreover, in each of the aforementioned patents, mechanical agitation means is utilized during oxidation. Not only do they require costly energy, i.e. utilities, to operate, but have the additional disadvantages of moving parts within the reactor, such as mechanical breakdowns. Other currently used oxidation reactors in which agitation is not provided suffer from significant temperature variations within the reactor and/or poor heat transfer characteristics, resulting in increased operating costs and lower product quality.
Reactors wherein circulation is induced without the need for an outside power source, e.g. electricity, or mechanical agitation are known. Liquid phase reactors, wherein the introduction of a gas to one part of the reactor induces circulation due to density differentiations, have been utilized for contacting liquid and solid particles. For example, U.S. Pat. No. 3,759,669, teaches a reactor with concentric reactor legs, in which introduction of gas maintains catalytic particles in suspension without the need of a circulating pump system. U.S. Pat. No. 3,552,934, uses a partition head with a plurality of channels to separate two such reactor legs or zones. U.S. Pat. No. 3,124,518 teaches a reactor configuration for hydrogenation, wherein the introduction of hydrogen induces the necessary circulation without mechanical agitation or stirring.